Dietary supplements can provide compounds and nutrients in addition to those found in a person's normal diet. In some cases, dietary supplements include more common nutrients that may already be present in a person's diet. For example, vitamin C is a common nutrient that some people believe, if taken in increased amounts, will aid in fighting the common cold or flu. Similarly, some compounds that exhibit antioxidant properties are consumed with the belief that they can provide increased lifespan and/or provide protection against certain diseases, such as cancer. Dietary supplements can be useful to ensure a person receives a full complement of the vitamins, minerals, and other nutrients recommended by doctors and nutritionists.